Highly active microleaves derived from MIL-101(Fe) through acid etching for improved visible light nitrogen reduction

Abstract

In this work, MIL-101(Fe) was etched with nitric acid to create biomimetic microleaf architectures for improved photocatalytic ammonia synthesis. The etching process is controlled by the concentration of acid molecules passing through the MOFs windows, allowing precise tuning of the inherent crystallinity and external morphology of the resulting catalysts. Notably, at the optimal acid concentration, the resulting catalyst forms microleaf structures less than 5 µm in length, growing together at one end. This catalyst achieves a visible light photocatalytic ammonia yield rate of 8.2 mmol g_cat⁻¹ after 4 h irradiation with an apparent quantum efficiency of 6.58 % at 420 nm. Moreover, the stable generation of ammonia using seawater, tap water, lake water, and turbid water without sacrificial reagents highlights the potential of the microleaf-shaped materials as a commercially viable photocatalytic system. Further mechanistic studies reveal that the deficient iron centers promote the chemisorption of nitrogen molecules and photoinduced electron transfer. The nitro groups incorporated through nitration may aid in forming the vein-like microleaf structure which not only exposes more active sites but also enhances the interaction between reactants and the catalyst surface. This work presents a promising strategy for synthesizing MOFs-derived hierarchical architectures for energy and environmental applications.